ABSTRACT : Following an episode of reduction in inspired oxygen concentration (FiO2) and inhalational agent concentration (Fi agent) during the changing of a soda lime absorber in the intraoperative period, We conducted an in vitro experiment to understand the impact of disconnection of the absorber on inspired gas dilution at different fresh gas flows (FGF) in Drägeranaesthesia work stations.

METHODS : We conducted an in vitro experiment to study the effect of disconnection of the soda lime absorber in Drägeranaesthesia work stations on FiO2 and Fi agent at different FGF. We connected a Siemens test lung to the breathing circuit and set the FGF at 8 L/min with oxygen and nitrous oxide (1:1) and isoflurane(1%). PPV was initiated at a TV of 500 ml, RR of 12/min. The inspired O2, N2O, and isoflurane concentrations were noted. The observations were noted after disconnecting the soda lime absorber and stabilized values for 3 minutes. The same experiment was repeated at 6 L/min, 4 L/min, 2 L/min and 1 L/min of FGF.

RESULTS : There was a fall in the FiO2 and Fi agent with the disconnection of the absorber (P<0.01). The magnitude of fall increased with the decrease in the FGF (P<0.05). The software SPSS 16.0 was used for analysis.

CONCLUSIONS : The operating principle of fresh gas decoupling valve is a potential source of this fall in the FiO2 and Fi agent, which must be kept in mind while changing the soda lime during the course of surgery where an anaesthetic work stations utilizing fresh gas decoupling valves are used.Anaesthesiologists who use modern workstations need to be educated about their principles of operation. In modern anaesthesia machines there is a chance for air dilution of inspired gases whenever the CO2 absorber is removed for refilling during the course of surgery.